Unshielded twisted pair (UTP) cable is popular for analog and digital data transmission. It consists of a multiplicity of twisted pair wires arranged in a specific grouping—typically four pairs to a jacketed bundle (see FIG. 1A).
FIGS. 1A and 1B illustrate prior art Unshielded Twisted Pair (UTP) cable for data transmission. As illustrated in FIG. 1A, a typical UTP cable 100 comprises four twisted pair wires 104, 106, 108, and 110, all located within a cable bundle. The bundled twisted pair wires are held together with insulation layer 102. Each of the four twisted pairs (e.g. 104, 106, 108 or 110) consists of two wires identified with suffix “A” and “B” and twisted together to form one conductor pair. For example, as illustrated in FIG. 1B, twisted pair conductor 104 comprises wire 104A and wire 104B. Twisted pair 106, twisted pair 108, and twisted pair 110 are also similarly configured.
As illustrated in FIG. 1B, a cross-sectional view of a twisted pair conductor shows two insulated wires in a side-by-side mechanical configuration. In actual practice, the twisted pair rotates the position of the two wires in an intimate helical pattern throughout the traverse of the pair length. Therefore, the twisted pair occupies an overall outer diameter equal to the sum of the diameters of both insulated wires (i.e. shown in dashed lines) even though an instantaneous view shows them to occupy a basically rectangular space.
Twisted pair wires are typically employed to transfer electrical information in the balanced line mode where one wire conveys current in one direction of an alternating current cycle while the second wire of the pair conducts current in the opposite direction of that alternating current cycle; i.e. 180 degrees out of phase. Balanced line operation affords better rejection of outside interference and noise due to normal cancellation in the differential receiver.
From an electrical point-of-view, the basic twisted pair is not shielded (i.e. UTP) and is susceptible to outside interference, crosstalk from other pairs, etc. Further, the magnetic field between the conductors of a twisted pair is concentrated within the aerial region between the two conductors, but is largely considered an external field capable of radiating energy depending on the frequency of operation. A shield can, and often is, added over the twisted pairs at additional cost, size, weight, and complexity. A shielded twisted pair (STP) cable offers distinct advantages over the unshielded variety with minimization of inter-pair crosstalk being one of the greatest advantages. STP cables are finding use in higher speed data applications like Category 7 (10 Gigabit Ethernet) network cabling.
Prior art UTP cable bundles wherein multiple (e.g. 4) twisted pairs are utilized, involve manipulation of the twisted pairs such that each pair has a different twist rate and maintains the same twist rate throughout the cable length so as to minimize crosstalk of data signals between pairs.
For example, each of the prior art twisted pair cables (e.g. 104, 106, 108, or 110) will have a specific twist rate different from the other twisted pairs. All of these twisted pairs, each one made with a specific twist rate, are located side-by-side within the cable bundle. The different twist rates contribute to lowered crosstalk but also contribute to skew (i.e. delay) between the conductor pairs because of the difference in length incident to the different twist rates.
Some prior art technologies employ other means to minimize crosstalk (or coupling). For instance, there are UTP cables constructed such that two pairs of the typically four pairs are twisted in a right-hand direction while the remaining two pairs are twisted in the usual left-hand direction. This configuration further minimizes crosstalk between data signals traveling on the cable pairs.
Twisted pairs are simply made by locating two separate insulated wires in close proximity and then rotating them about one another to create the rolling twist geometry. Twisted pair wire is inexpensive and relatively easy to produce. However, the data networks and many analog applications utilizing twisted pair cable put new demands on twisted pair cable construction. Challenges encountered in making twisted pair cables include: maintenance of a constant twist rate to control intra-pair signal skew; maintenance of a constant, or deliberate, twist rate relationship between pairs in a bundle so as to control pair crosstalk; and control of physical geometry and positioning of the twisted pairs such that cable attenuation characteristics and crosstalk rejection is controlled.
Therefore there is a need for cabling that can be manufactured without the challenges of prior art UTP cable bundles, cheaper than STP cables, and provides benefit similar or better than STP cables, e.g. minimum skew and cross-talk during transmission of data signals.